Self-crosslinking powder containing carboxy and epoxy groups admixed with a flow control agent

ABSTRACT

POWDER COATING COMPOSITIONS ARE DISCLOSED IN GENERAL. INDIVIDUAL POWDER COATING COMPOSITIONS OF THIS INVENTION ARE A MIXTURE A SEVERAL MATERIALS. THE MOST SIGNIFICANT MATERIALS EMPLOYED IN THE POWDER COATINGS INCLUDE THE FOLLOWING. A COPOLYMER CONTAINING CROSSLINKABLE, FUNCTIONAL GROUPS. FORMS THE MOST IMPORTANT CONSTITUENT OF THE POWDER COATING. THE COPOLYMER HAS A GLASS TRANSITION TEMPERA TURE IN THE RANGE OF 40*C TO 90*C AND A MOLECULAR WEIGHT (MN) IN THE RANGE FROM ABOUT 2,000 TO ABOUT 15,000. ANOTHER MATERIAL OF AN INDIVIDUAL COMPOSITION IS A FLOW CONTROL AGENT WHICH FORMS AT LEAST 0.05% BY WEIGHT OF THE MIXTURE. THE FLOW CONTROL AGENT IS A POLYMER HAVING A MOLECULAR WEIGHT (MN) OF AT LEAST 1000. ALSO, THE FLOW CONTROL AGENT HAS A GLASS TRANSITION TEMPERATURE AT LEAST 50*C. LOWER THAN THE GLASS TRANSITION TEMPERATURE OF THE COPOLYMER. OTHER MATERIALS WHICH MAY BE EMPLOYED IN INDIVIDUAL POWDER COATING COMPOSITIONS ARE CATALYSTS, PIGMENTS, ANTISTAIC AGENTS AND PLASTICIZERS.

United States Patent US. Cl. 260836 4 Claims ABSTRACT OF THE DISCLOSURE Powder coating compositions are disclosed. In general, individual powder coating compositions of this invention are a mixture of several materials. The most significant materials employed in the powder coatings include the following. A copolymer containing crosslinkable, functional groups, forms the most important constituent of the powder coating. This copolymer has a glass transition temperature in the range of 40 C. to 90 C. and a molecular weight (31,) in the range from about 2,000 to about 15,000. Another material of an individual composition is a flow control agent which forms at least 0.05% by weight of the mixture. The flow control agent is a polymer having a molecular weight (M of at least 1000. Also, the flow control agent has a glass transition temperature at least 50 C. lower than the glass transition temperature of the copolymer. Other materials which may be employed in individual powder coating compositions are catalysts, pigments, antistatic agents and plasticizers.

BACKGROUND OF THE "INVENTION Powder coating composition for use in the painting of surfaces are extremely desirable. Such coating compositions are desirable because they eliminate the solvents utilized in liquid paint systems, as for example, the paint system shown in US. Pat. 2,857,354 issued Oct. 21, 1958. A powder coating paint composition is curable by heat in a manner that little, if any, volatile material is given off to the environment. This, of course, is substantially different from a liquid paint system as the liquid paint vehicle must be volatilized during the drying of the paint. Volatilization of the liquid vehicle carries such vaporized material into the ambient.

This invention is directed to powder coating compositions which are suitable for finishing surfaces of articles with a protective and decorative coating. The coating produced by the compositions of this invention are comparable on all terms with the coating produced by prior art liquid paint systems. The liquid paint system disclosed in US. Pat. 2,857,354 is apparently similar, but in reality, substantially different than the powder coating compositions of this invention. The full discussion of these differences is set forth in the last portion of this specification.

SUMMARY OF THE INVENTION Ths invention is directed to powder coating compositions and, more particularly, to powder coating compositions which are curable by heat and which do not contain external crosslinking agents. Individual ones of the powder coating compositions formed in accordance with the teachings of this invention comprise an intimate mixture of several materials. Materials such as antistatic agents, catalysts, plasticizers and pigment may be included in individual compositions to acheve desired effects. Another material, which is of significant mportance, and whch is included in each individual powder coating composition, is a copolymer containing crosslinkable, functional groups. This copolymer has a glass transition temperature in the ice range of 40 C. to C. and a molecular weight (M,,) in the range from about 2,000 to about 15,000. In greater detail, the copolymer may contain, for example (a) approximately stoichiometric quantities of functional, ethylenically unsaturated monomers, one containing epoxy functional groups and the other carboxy functional groups, and (b) ethylenically unsaturated monomers containing no functional groups and so selected that when both types of the monomers are reacted to produce the copolymer, the copolymer will have the glass transition temperature and molecular weight mentioned.

Another significant material employed in individual powder coating compositions of this invention is a flow control agent whch forms at least 0.05% by weight of the total mixture. The flow control agent is a polymer having a molecular weight (H,,) of at least 1000. The flow con trol agent has a glass transition temperature at least 50 C. below the glass transition temperature of the copolymer.

As previously mentioned, a powder coating composition formed in accordance with the teachings of this invention may include a small weight percentage of a catalyst. Generally, the catalyst is selected to produce a gel time for the powder coating composition greater than one minute at the baking temperature of the composition. The coating composition may also use therein a pigment which can form from about 6% by weight to about 35% by weight of the total mixture depending on the pigment selected. The powder coating composition may also include a small weight percentage of an antistatic agent so that the composition may be applied in an electrostatic spray operation.

Some particular materials which have been found suitable for use in making powder coating compositions in accordance with the teachings of this invention are set forth below. The materials are representative of the various types of material which may be used but individual powder coating compositions of this invention are not limited to these specific materials.

The copolymer of the coating composition should contain from about 2% by weight to about 10% by weight of the monomer supplying the epoxy functional groups to the copolymer. The monomer supplying the carboxy functional groups should be present in the copolymer in the range from about 2% by weight to about 8% by weight. Glycidyl methacrylate and glycidyl acrylate are monomers which are suitable for supplying the epoxy functional groups. The carboxy functional groups may be supplied by monomers such as methacrylic acid and acrylic acid. The monomers containing the functional groups are mixed with other, nonfunctional group containing monomers in order to form a copolymer having the desired glass transition temperature range and molecular weight range. Some monomers which are suitable for this purpose are methyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, styrene, alpha methyl styrene, acrylonitrile, methacrylonitrile, etc.

With respect to the flow control agents used in the powder coating mixture, an individual agent selected for a mixture may be an acrylic polymer having a glass transition temperature at least 50 C. below the glass transition temperature of the mixtures copolymer. Preferred acrylic polymers which may be used as the flow control agent are polylauryl acrylate, polybutyl acrylate, poly (Z-ethylhexyl acrylate), polylauryl methacrylate and polyisodecyl methacrylate.

The flow control agent may also be a fiuorinated poly mer having a glass transition temperature at least 50 C. below the glass transition temperature of the copolymer utilized in the mixture. Preferred flow control agents, if the agent is a fiuorinated polymer, are esters of polyethyleneglycol or polypropyleneglycol and fiuorinated fatty acids. For example, an ester of polyethyleneglycol of molecular weight of over 2500 and perfiuoro octanoic acid is useful as a flow control polymer.

A small weight percentage of a catalyst may be added to the powder coating composition in order to increase the crosslinking rate of the powder coating composition at the baking temperature thereof. In preference, the catalyst produces a gel time for the powder coating composition of at least 1 minute but no greater than 40 minutes. The preferred catalyst is one which produces a gel time of at least 1 minute but no greater than minutes. In general, the catalyst is present in the range of from 0.05% by weight to 1% by weight of the weight of the mixture. The most desirable gel time produced by the catalyst is in a time range of from about 2 minutes to about 6 minutes. These catalyst gel times are at baking temperatures for the powder coating compositions in the range of 130 C. to 200 C.

The powder coating compositions of this invention may also contain from about 6% by weight to about 35% by weight of a pigment. The various pigments already known in the art may be employed in the powder coating compositions. The pigments are generally selected for color, appearance and/or corrosion protection properties.

A small weight percent of an antistatic agent may also be employed in the powder coating composition. For example, 0.01% by weight to 0.3% by weight of the powder coating composition may be an antistatic agent so that the coating may be applied in an electrostatic spraying operation.

The powder coating compositions of this invention may also contain a plasticizer. If used, the plasticizer is present from about 2% by weight to about 10% by weight of the powder.

DESCRIPTION OF THE PREFERRED EMBODIMENT A general discussion of the various materials which may be employed in the powder coating compositions of this invention will be set forth below. Also, a plurality of examples will be employed to show the manner in which various, individual, powder coating compositions, which fall within the scope of this invention are prepared and utilized.

The principal material in individual powder coating compositions is the copolymer containing crosslinkable, functional groups. The copolymer is so formed that it has a glass transition temperature in the range of 40 C. to 90 C. and a molecular weight (Ti in the range from about 2,000 to about 15,000. The copolymer is generally formed from (a) functional monomers containing epoxy functional groups and carboxy functional groups and (b) modifying monomers containing no functional groups (after copolymerization) and so selected that the copolymer has the glass transition temperature and the molecular weight described. Particular powder coating compositions are made from a copolymer which is formed by reacting (a) approximately stoichiometric quantities of two ethylenically unsaturated monomers, one containing epoxy functional groups and the other containing carboxy functional groups with (b) ethylenically unsaturated monomers containing no functional groups.

Glycidyl methacrylate and glycidyl acrylate are particularly desirable monomers for forming the epoxy supplying monomer for the copolymer. When these materials are used, they are present in the copolymer from about 2% by weight to about 10% by weight.

Methacrylic acid and acrylic acid are particularly desirable monomers for forming the carboxy supplying monomer for the copolymer. When these materials are used, they are present in the copolymer from about 2% by weight to about 8 by weight.

The nonfunctional monomers which may be reacted with the functional monomers to produce the copolymer having the stated glass transition temperature and molecular weight are many in number. Some of the preferred nonfunctional monomers are methyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, styrene, alpha methyl styrene, acrylonitrile and methacrylonitrile.

The copolymers can be prepared by a variety of methods. Generally, a free radical initiator is needed to induce polymerization reaction. A large number of free radical initiators are known in the art. These include benzoyl peroxide, lauryl peroxide, t-butylhydroxyperoxide, acetylcyclohexane sulfonyl peroxide, diisobutyryl peroxide, di-(Z- ethylhexyl) peroxydicarbonate, diisopropyl peroxydicarbonate, t-butylperoxypivalate, decanoyl peroxide, azobis (2-methylpr0pi0nitrile), etc. The polymerization is preferably carried out in solution using a solvent in which the copolymer is soluble. Toluene, benzene, xylene, dioxane, butanone, etc., are suitable solvents for polymerization. If the copolymer is prepared in solution it can be used in that form or the solid copolymer can be obtained by evaporating the solvent under vacuum or spray drying techniques. Alternatively, the copolymer can be precipitated by pouring the copolymer solution at a slow rate into a non-solvent liquid such as hexane, octane or water under a suitable agitation condition. The copolymer thus obtained can then be dried so that it contains less than 3% of the volatile liquids.

The copolymers can also be prepared by emulsion polymerization, suspension polymerization, bulk polymerization or their suitable combination. In these methods of preparing the copolymers, chain transfer agents may be required to control the molecular weight of the copolymer to a desired range.

For powder coating applications, molecular weight and molecular weight distribution of the copolymer is important. Copolymer of average molecular weight (i in the range of 2,000 to 10,000 are suitable. These 00- polymers, however, must not contain significant amount of higher molecular weight fractions. No more than 2% of the copolymer can be of molecular weight greater than 20,000. The molecular weight distribution as measured by the ratio of weight average molecular weight to number average molecular weight (M /fi should be in the range of 1.6 to 2.1. The preferred range of molecu lar weight distribution is in the range of 1.7 to 1.8.

A flow control agent is also included in forming each individual one of the powder coating compositions of this invention. The flow control agent forms at least 0.05% by weight of an individual powder coating. The flow control agent generally does not exceed about 4% by weight of any individual powder coating composition. In general, the flow control agent is a polymer having a molecular weight (fi of at least 1000. Further, the flow control agent has a glass transition temperature at least 50 C. below the glass transition temperature of the copolymer employed in forming the composition.

One type of material which is used as a flow control agent in the powder coating compositions is an acrylic polymer having a glass transition temperature at least 50 C. below the glass transition temperature of the compositions copolymer. Some acrylic polymers which are preferred as flow control agents are polylauryl acrylate, polybutyl acrylate and poly(Z-ethylhexyl acrylate). Acrylic polymers to be used as flow control agents can be prepared by polymerization of the acrylate or methacrylate monomers in bulk or in suitable solvent using well known free radical initiators. The amount of the initiator and the polymerization conditions are chosen so that polymer formed has molecular weight (fi above 1000. The preferred molecular weight range of the acrylate polymer is above 5000. The most preferred range of the acrylate polymer is 6,000 to 20,000.

Although polymeric acrylate flow control agents are preferred, fluorinated polymers have been found to act as flow control agents for the powder coating compositions. Such fiuorinated polymers are esters of polyethyleneglycol or polypropylene glycol and fluorinated fatty acids. Esters of polyethylene glycol of molecular weight (fi of over 2500 and perfluoro octanoic acid are useful as flow control agents for the compositions of this invention.

The compositions of this invention can each contain a small, effective, weight percentage of a catalyst. In general, the catalyst is present in an individual composition in a range from 0.05% by weight to 1.0% by weight. The catalyst is selected to produce a gel time for the powder coating composition greater than at least 1 minute at the baking temperature of the composition. A suitable catalyst is also one which will produce a gel time that does not exceed 40 minutes. As used herein, the gel time of a coating composition is that time in which the coating composition develops elasticity and resistance to flow at the baking temperature.

Some catalysts which are suitable for use in the powder coating composition include tetralkylammonium salts, imidazole type catalysts, tertiary amines, triaryl phosphates and metal salts or organic carboxylic acids. The tetralkylammonium salts catalysts include the following: tetrabutyl ammonium chloride (bromide or iodide), tetraethyl ammonium chloride (bromide or iodide), tetramethyl ammonium chloride, dodecyl dimethyl (2-phenoxyethyl) ammonium bromide and diethyl (2-hydroxy ethyl) methyl ammonium bromide. Suitable catalysts of the imidazole type include: 2-methyl-4-ethyl imidazole, 2-methyl imidazole, imidazole, 2-[(N-benzylanilino) methyl]-2-imidazoline phosphate, and 2-benzyl-2-imidazoline hydrochloride. Suitable tertiary amine catalyst for the powder coating compositions of this invention include: trithylenediamine, N,N-diethylcyclohexylamine, and N- methyl morpholine. The metal salts of organic carboxylic acid which are catalyst for the powder coatings of this invention include, but are not limited to: stannous octoate, zinc naphthenate, cobalt naphthenate, zinc octoate, stannous 2-ethylhexoate, phenylmercuric propionate, lead enodecanoate, dibutyl tin dilaurate and lithium benzoate. An example of triarylphosphate type catalyst is triphenylphosphate.

The catalyst used in an individual powder coating composition is preferably solid at room temperature and has a melting point of from 50 C. to 200 C. As previously specified, the catalyst is present in a powder coating composition from 0.05% by weight to 1.0%. by weight of the total weight of the powder composition. Further, the catalyst produces a gel time of at least 1 minute and no greater than 40 minutes. Generally, the preferred gel time of the composition is in the range of from 1 minute to approximately 6 minutes at the baking temperature of the composition.

Since individual powder coating compositions of this invention can be applied to an article to be painted by electrostatic methods, it is preferred to include a small weight percentage of an antistatic agent in such compositions so that the deposition thereof is accomplished in a proper manner. In particular, the antistatic agent is included in a range from 0.01% to 0.3% by weight of the total powder composition. Suitable antistatic agents include, but are not limited to, tetralkylammonium salts as discussed previously and which also serve as catalyst. Other suitable antistatic agents include: alkyl-poly (ethyleneoxy) phosphates as, for example, dibutylpoly (ethyleneoxy) phosphate or alkylaryl poly (ethyleneoxy) phosphates as for example, ethyl benzyl poly (ethyleneoxy) phosphate, pyridine hydrochloride or inorganic salts such as lithium perchlorate.

In order to give individual powder coating compositions of this invention a suitable color, a pigment is included in the coating composition. In general, the pig merit forms from about 6% by weight to about 35% by weight of the total powder coating composition. Pigments which are suitable for powder coating compositions include, but are not limited to, the following: basic lead silico chromate 30% by weight (orange); titanium dioxide 30% by weight (white); titanium dioxide 15% by weight plus ultra marine blue 10% by weight (blue); phthalocyanine blue 7% by weight plus titanium dioxide 10% by weight (blue); phthalocyanine green 7% by weight plus titanium dioxide 10% by weight (green); ferrite yellow 7% by weight plus titanium dioxide 10% by, weight (yellow); carbon black pigment 6% by weight (black); black iron oxide 10% by weight (black); chromium green oxide 8% by weight plus titanium dioxide 10% by weight (green); quindo red 5% by weight plus titanium dioxide 16% by weight (red); and iron oxide transparent orange pigment 10% by weight (orange).

A plasticizer may be used in a powder coating composition of this invention if desired. The type of plasticizers used very often include adipates, phosphates, phthalates, sebacates, polyesters derived from adipic acid or azelaic acid, and epoxy or epoxidized plasticizers. Some of these plasticizers are; adipates: di(n-hexyl) adipate, diisooctyl adipate, dicyclohexyl adipate; phosphates: triphenylphosphate, tricreylphosphate, tributylphoshpate; phthalates; dibutylphthalate, dioctylphthalate, butyl octyl phthalate; and sebacates: dioctyl sebacate, butyl benzyl sebacate, and dibenzyl sebacate.

Having generally described the various materials which are employed in formulating the powder coating composition of this invention, a plurality of examples will be set forth to illustrate various individual powder coating compositions.

EXAMPLE 1 The monomers, glycidyl methacrylate 30 grams, methacrylic acid 21 grams, methyl methacrylate 129 grams, butyl methacrylate 120 grams, and the initiator t-butylperoxypivate 12 grams is formed into a mixture. Three hundred grams of benzene is charged into a one liter flask which is equipped with a dropping funnel, condenser, stirrer, thermometer and nitrogen inlet. The mono mer mixture is placed in the dropping funnel. The flask is heated to C. and a refluxing of the solvent is achieved. While maintaining the reaction temperature at 80 C., the monomer mixture is added in a dropwise fashion over a two hour period. After the additions is complete, the reaction is continued for another two hours. The contents of the flask is then cooled to room temperature.

One hundred ml. of the monomer solution is mixed with: titanium dioxide 4.6 grams, ferrite yellow 5.7 grams, poly (2-ethylhexyl acrylate) (M,,) :-00, 0.3 gram. The mixture is dispersed and then is dried in a vacuum oven at 70 C. The powder coating obtained is ground to pass through a 200 mesh sieve.

The resulting powder thus obtained is a powder coating composition of the invention. The powder is sprayed onto an electrically grounded, steel panel by using electrostatic powder spray gun operating at 50 kv. charging voltage. After spraying, the panel is heated at 175 C. for 20 minutes.

The coating obtained on the panel has good adhesion to the steel panel and good impact strength. The coating also is applied to and has good adhesion on panels of glass, brass, zinc, aluminum, copper and bronze. The coating obtained is not soluble in toluene, gasoline, butanone or methanol.

EXAMPLE 2 The monomers, glycidyl methacrylate 9 grams, methacrylic acid 6 grams, methyl methacrylate 150 grams, butyl methacrylate grams, and the initiator 2,2- azobis (Z-methylpropionitrile) (AIBN) are formed into a mixture. The mixture is reacted in accordance with the procedure of Example 1. The cooled, reacted mixture, however, is spray dried at 60 C. air temperature.

7 The spray dried powder is ground to pass through a 100 mesh screen.

One hundred parts by weight of the ground copolymer are mixed with the following materials:

Parts Tetrabutyl ammonium bromide 0.1 Polylauryl acrylate (M :10,000) 0.5 Titanium dioxide 30 The materials are mixed together in a ball mill for 2 hours. The mixture is milled rolled at 85 C. to 90 C. for minutes. The solid obtained is ground in a ball mill to pass through a 140 mesh screen.

The resulting powder thus obtained is a powder coating composition of the invention. The powder is sprayed on an electrically grounded, steel panel by using electrostatic powder spray gun operating at 50 kv. charging voltage. After spraying, the panel is heated at 175 C. for 20 minutes.

The coating obtained on the panel has good adhesion to the steel panel and good impact strength. The coating also is applied to and has good adhesion on panels of glass, brass, zinc, aluminum, copper and bronze. The coating obtained is not soluble in toluene, gasoline, butanone or methanol.

EXAMPLE 3 The monomers, allyl glycidyl ether 18 grams, methacrylic acid 12 grams, methyl methacrylate 135 grams, butyl methacrylate 135 grams, and the initiator AIBN 12 grams are reacted and processed as described in Example 2 to produce a ground copolymer. One hundred parts of the copolymer produced is mixed with the same additional ingredients described in Example 2.

The powder coating composition obtained by following the process steps set forth in Example 2 is applied to test panels in the same manner as described in Example 2. The coating is baked at a temperature of 170 C. for 30 minutes. The coating obtained has good adhesion to steel, glass, brass, zinc, aluminum, copper and bronze.

EXAMPLE 4 The monomers, glycidyl methacrylate 18 grams, acrylic acid 9 grams, methyl methacrylate 100 grams, acrylonitrile 50 grams, butyl methacrylate 123 grams, and the initiator t-butylperoxypivalate 12 grams are reacted and processed as described in Example 2 to produce a ground copolymer.

The ground copolymer (100 parts by weight) is added to the following materials:

Parts Tetrabutyl ammonium chloride 0.1 Polybutylacrylate (fi =9000) 4 Titanium dioxide 15 Ultra marine blue 10 The above ingredients are mixed together and processed in accordance with the procedure of Example 2 to obtain a powder coating composition. The powder coating composition is sprayed on various test panels of steel, glass, brass, zinc, aluminum, copper and bronze. The coating obtained on each test panel after curing of the powder coating composition at a temperature of 200 C. for 10 minutes is of good quality, and is solvent and scratch resistant.

EXAMPLE 5 The monomers, glycidyl methacrylate 18 grams, acrylic acid 9 grams, methyl methacrylate 160 grams, methacrylonitrile 54 grams, butyl acrylate 69 grams, and the initiator t-butylperoxypivalate 9 grams are reacted in accordance with the procedure of Example 1. The cooled, reacted mixture, however, is vacuum dried at 60 C. The dried powder is then ground to pass through a 100 mesh screen.

One hundred parts by weight of the copolymer obtained is mixed with the following materials:

Parts 2methyl-4ethylimidazole 0.05 Dibutyl poly(ethyleneoxy)phosphate 0.05 Polyisododecylmethacrylate 4 Titanium dioxide 10 Phthalocyanine blue 7 A powder coating composition is obtained by following the process steps set forth in Example 2. The coating composition is applied to a series of test panels and baked at the temperature of and for the same time as Example 4. The coating obtained on the various test panels is of good quality with respect to its adhesion appearance and impact characteristics.

EXAMPLE 6 A monomer mixture having the following composition is prepared: glycidyl methacrylate 30 grams, methacrylic acid 21 grams, styrene grams, butyl methacrylate 129 grams, and the initiator t-butylperoxypivalate 9 grams. This mixture is reacted and processed as described in Example 5 to produce a ground copolymer.

One hundred parts by weight of the copolymer obtained is added to the following materials:

Parts Triethylene diamine 0.05 Tetraethylammonium chloride .05 Polyaurylmethacrylate (fi 6000) 2 Phthaloycanine green 7 Titanium dioxide 10 The above described materials are processed as described in Example 2 in order to produce a powder coating composition. The powder coating composition is applied to test panels as described in Example 2 and baked on the panels at a temperature of C. for 15 minutes.

The coating obtained has good adhesion to steel, glass, brass, Zinc, aluminum, copper and bronze and is insoluble in toluene, gasoline, methanol and butanone.

EXAMPLE 7 Parts Tetramethyl ammonium chloride l Poly(2-ethylhexyl acrylate) (H =20,'000) 2 Ferrite yellow 7 Titanium dioxide 10 This mixture is processed as described in Example 2 in order to form a powder coating composition. The powder coating composition is applied to test panels as clescribed in Example 2. The panels are baked at a temperature of 180 C. for 5 minutes. The adhesion quality of the powder coating after baking on the various test panels is good. The coating on each panel possesses good solvent and scratch resistance.

EXAMPLE 8 A monomer mixture having the following composition is prepared: glycidyl methacrylate 30 grams, acrylic acid 15 grams, styrene grams, ethyl acrylate 90 grams, and the initiator AIBN 6 grams. The mixture is reacted and processed as described in Example 2 to produce a ground copolymer.

One hundred parts of the ground copolymer obtained is added to the following materials:

'Parts Trimethyl benzyl ammonium chloride 0.1

Poly(2-ethylhexyl acrylate) (fi =11,000) 2 Carbon black 6 The above materials are mixed and processed as set forth in Example 2. The resulting powder coating composition is applied to test panels as specified in Example 2. The coating composition is baked at 170 C. for 15 minutes. All the painted panels exhibit good adhesion and solvent resistance properties.

EXAMPLE 9 A monomer mixture having the following composition is prepared: glycidyl methacrylate 6 grams, methacrylic acid 3.5 grams, methyl methacrylate 150.5 grams, butyl methacrylate 140 grams, and the initiator AI'BN 9 grams. The mixture is reacted and processed as described in Example 2 to produce a ground copolymer.

One hundred parts of the ground copolymer obtained is added to the following materials:

Parts Dodecyldimethyl (2-phenoxy-ethyl) ammonium bromide 0.5 Polyethylene glycol perfluoro octanoate (101 :3400)- 2 Black iron oxide 1 Butyl benzyl phthalate 3 The mixture so formed is processed as described in Example 2 to produce a powder coating composition. This powder coating composition is applied to test panels as it is described in Example 2. The coated panels are baked at 165 C. for 15 minutes. The coating on each panel has good adhesion and solvent resistance.

EXAMPLE 10 A monomer mixture having the following composition is prepared: glycidyl methacrylate 12 grams, methacrylic acid 7 grams, methyl methacrylate 148 grams, butyl methacrylate 200 grams, lauryl methacrylate 33 grams, and the initiator AIBN 12 grams. The mixture is reacted and processed as described in Example to produce a ground copolymer.

One hundred parts by weight of the ground copolymer is mixed with the following materials:

Parts Tetraethylammonium bromide 0.2 Ethyl benzyl(ethyleneoxy) phosphate 0.5 Poly (2-ethylhexyl acrylate) (H =1500) 0.4 Chromium green oxide 8 Titanium dioxide 10 Dioctyl sebacate 7 The above mixture is processed as described in Example 2 to produce a powder coating composition. The powder coating composition is applied to a plurality of test panels as is described in Example 2. The panels are baked at a temperature of 170 C. for minutes. The adhesion to the test panels of the powder coating material is good.

EXAMPLE 11 A monomer mixture having the following composition is prepared: glycidyl methacrylate 12 grams, methacrylic acid 7 grams, methyl methacrylate 85 grams, cyclohexyl methacrylate 8 grams, butyl methacrylate 188 grams, and the initiator AIBN 12 grams. The mixture is reacted and processed as described in Example 2 to produce a ground copolymer.

10 One hundred parts by weight of the ground copolymer is mixed with the following materials:

Parts Stannous octoate 0.1 Tetraethylammonium bromide .05 Polyethylene glycol perfluoro octonoate 2 Quindo red 5 Titanium dioxide 15 The mixture above described is processed as set forth in Example 2 to produce a powder coating composition. The powder coating composition is applied to test panels as described in Example 2. The panels are baked at 150 C. for 20 minutes. The adhesion to the panels of the powder coating is good and the coating possesses good solvent resistance.

EXAMPLE 12 A monomer mixture having the following composition is prepared: glycidyl methacrylate 12 grams, methacrylic acid 7 grams, methyl methacrylate 273 grams, butyl methacrylate 8 grams, and the initiator AIBN 12 grams. The mixture is reacted and processed as described in Example 5 to product a ground copolymer.

The ground copolymer parts by weight) is added to the following materials:

Parts Zinc octoate 0.3 Tetrabutylammonium iodide 0.1 Polybutyl acrylate (fi =14,000) 2.0 Iron oxide transparent orange 10 The above ingredients are mixed together and processed in accordance with the procedure of Example 2 to obtain a powder coating composition. The powder coating composition is sprayed on various test panels of steel, glass, brass, zinc, aluminum, copper and bronze. The coating obtained on each test panel after curing of the powder coating composition at a temperature of C. for 20 minutes is of good quality, and is solvent and scratch resistant.

EXAMPLE 13 A monomer mixture having the following composition is prepared: glycidyl acrylate 12 grams, methacrylic acid 7 grams, methyl methacrylate 273 grams, butyl methacrylate 8 grams, and the initiator AIBN 12 grams. The mixture is reacted and processed as described in Example 2 to produce a ground copolymer.

The ground copolymer (100 parts by weight) is added to the following materials:

Parts Tetrabutylammonium bromide 0.2 Poly(2-ethylhexyl acrylate) (M =10,000) 3.5 Carbon black 6 The above ingredients are mixed together and processed in accordance with the procedure of Example 2 to obtain a powder coating composition. The powder coating composition is sprayed on various test panels as described in Example 2. The coating obtained on each test panel after curing of the powder coating composition at a temperature of C. for 10 minutes is of good quality. Also, the coating obtained on each test panel is insoluble in toluene, gasoline, methanol and butanone.

EXAMPLE 14 A monomer mixture having the following composition is prepared: glycidyl methacrylate 12 grams, methacrylic acid 12 grams, methyl methacrylate 130 grams, isobornyl methacrylate 18 grams, butyl methacrylate 230 grams, and the initiator AIBN 10 grams. The mixture is reacted and processed as described in Example 2 to produce a ground copolymer.

The ground copolymer (100 parts by weight) is added to the following materials:

Parts Tetrabutylammonium bromide 0.1 Polylauryl acrylate (fi =8000) 0.4 Titanium dioxide 30 Tricresyl phosphate The above ingredients are mixed together and processed in accordance with the procedure of Example 2 to obtain a powder coating composition. The powder coating composition is sprayed on various test panels of steel, brass, glass, zinc, aluminum, copper and bronze. The coating obtained on each test panel after curing of the powder coating composition at a temperature of 130 C. for minutes is of good quality and is solvent and scratch resistant.

EXAMPLE A polymer is prepared with the equipment described in Example 1 by dropping into 100 grams of refluxing toluene under a nitrogen atmosphere a mixture of 2- hydroxyethyl methacrylate 15 grams, methacrylic acid 8 grams, methyl methacrylate 40 grams, butyl methacrylate 37 grams, and the initiator AIBN 4 grams.

Refluxing is continued for 3 hours. The copolymer solution is then cooled to room temperature and poured into stainless steel trays. The solvent is evaporated under vacuum at 70 C. and the copolymer ground.

The ground copolymer (100 parts by weight) is then mixed with the following materials:

Parts Zinc chloride 1 Polybutyl acrylate (H =9000) 0.8 Titanium dioxide 9 Ferrite yellow 7 The mixture is mill rolled for 5 minutes at 90 C. and then ground to powder to pass through a 200 mesh screen. The powder is electrostatically sprayed on various test panels which are then baked at 200 C. for 30 minutes. The coatings on the test panels all have good appearance.

EXAMPLE 16 A three liter, four necked flask fitted with a stirrer, a condenser, a nitrogen inlet and a dropping funnel is charged with 450 grams of n-butanol and 300 grams of toluene. The flask is heated using a heated mantle so that the solvent mixture is refluxing. A mixture of styrene 500 grams, ethylacrylate 100 grams, diacetone acrylamide 100 grams, and benzoyl peroxide 28 grams is added slowly to the flask from the dropping funnel over a period of two hours. The reflux temperature is maintained for an additional two hour period. One hundred and thirty grams of n-butyl formcel (40% formaldehyde) and 4 grams of potassium hydroxide dissolved in grams of n-butanol is added. Reflux temperature is maintained for 6 more hours. The flask is then cooled to room temperature.

Two hundred grams of the polymer solution is mixed with titanium dioxide 10 grams, phthalocyanine blue 5 grams, polybutyl acrylate (M =10,000) 1 gram, and tetrabutyl ammonium bromide 0.4 gram. The mixture is agitated to achieve a pigment dispersion. The mixture is spray dried at 60 C. air temperature. The powder obtained is further dried under vacuum and sieved through a 200 mesh screen. The powder is then sprayed by electrostatic spray gun on various test panels and baked at 170 C. for minutes. An adherant coating with good properties is obtained on all test panels.

The use of glycidyl methacrylate copolymers and dicarboxylic acid cross linking agents in a liquid paint system is described in US. Pat. 2,857,354. However, the powder coating compositions of this invention are substantially dilferent than the liquid paint compositions described in the examples of that patent. This dilterence can be best illustrated by attempting to prepare powder coating compositions by evaporating the solvents from the liquid paint systems described in the examples of the patent. Dry powders cannot be prepared from the com positions of Examples 4 and 5 of the patent. Powders prepared from the compositions of Example 1, 2, 3 and 6, when deposited on a metal panel, do not fuse well together to form a film when the panels are baked at to 200 C. for 20 minutes. The baked coatings on test panels are not smooth, but rather, are rough and contain a large number of craters. Also, the baked coatings possess very low gloss, and have a lack of flexibility and adhesion. It, therefore, can be concluded that compositions which are generally suitable for liquid paint systems are not necessarily suitable for powder paints by simply evaporating the solvents therefrom.

The use of a dicarboxylic acid as a cross linking agent for glycidyl methacrylate terpolymers is mentioned in US. Pat. 3,058,947. In order to test these materials, compositions of Example VII of this patent are dried by evaporating solvents under vacuum. The materials are ground to pass through a 200 mesh screen. Samples of the ground powder are deposited on metal panels and baked at C. for 45 minutes. The coatings obtained show an abundance of craters, are inferior in gloss and smoothness, and lack the impact properties described in the Example VII. It is, therefore, concluded that there is a substantial dilference in paint films produced on a panel when the coating is produced on one hand by a liquid system, and, on the other hand, by a powder system. Other improvements specific to the powders are needed in order to obtain paints of acceptable quality. The reason for the difference between the properties and appearance of powder coatings derived by solvent evaporation from a liquid coating and the liquid coatings itself are not clear. It is, however, certain that the powders obtained by drying liquid paint compositions are not useful for powder coating compositions.

There has been disclosed herein powder coating compositions which may be employed in the painting of articles. Many modifications of this invention will be apparent to those skilled in the art in view of this specification. It is intended that all such modifications which fall within the scope of this invention be included within the appended claims.

What We claim is:

1. A powder coating composition which, exclusive of catalyst, pigment, plasticizer, and an antistatic agent, cornprises a mixture of:

(A) a copolymer containing (a) quantities of two monoethylenically unsaturated monomers, one monomer containing epoxy functional groups and being present in an amount of 2 to 10 percent by weight of the copolymer and the other monomer containing carboxy functional groups and being present in an amount of 2 to 8 percent by weight of the copolymer, and (b) ethylenically unsaturated monomers containing no functional groups and so selected that when both types of said monomers are reacted at their sites of unsaturation to form said copolymer, said copolymer will have a glass transition temperature in the range of 40 C. to 90 C. and a molecular weight (TL) in the range of 2,000 to about 15,000; and

(B) a flow control agent forming from at least about 0.05% to about 4.0% by weight of the mixture, said flow control agent being a polymer or a copolymer having a molecular Weight (M of at least 1000, said flow control agent being selected from the group consisting of acrylate esters, methacrylate esters and polyethylene or polypropylene glycol esters of fluorinated fatty acids.

2. A powder coating composition comprising a mixture of:

(A) a copolymer formed from (a) of a monomer containing epoxy functional groups selected from the group consisting of glycidyl methacrylate and glycidyl acrylate and being present in an amount of 2 to percent by weight of the copolymer and a monomer containing carboxy functional groups selected from the group consisting of methacrylic acid and acrylic acid, and being present in an amount of 2 to 8 percent by weight of the copolymer, said copolymer also containing (b) monethylenically unsaturated modifying monomers having no functional grorps and so selected that said copolymer has a glass transition temperature of from 40 C. to about 90 C. and a molecular weight (fi in the range from about 2,000 to about 10,000;

(B) a flow control agent forming from at least 0.05% to about 4.0% by weight of the mixture, said flow control agent being a polymer or a copolymer having a molecular weight (lT of at least 1000, said flow control agent being selected from the group consisting of acrylate esters, methacrylate esters and polyethylene or polypropylene glycol esters of fluorinated fatty acids; and

(C) a small weight percent of a catalyst which produces a gel time for the powder coating composition greater than one minute at the baking temperature of the composition.

3. The powder coating composition of claim 2 wherein: said modifying monomers are selected from the group consisting of methyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexy1 acrylate, styrene, alpha methyl styrene, acrylonitrile, and methacrylonitrile.

4. The powder coating composition of claim 2 wherein: a pigment is included which forms from about 6% by weight to about by weight of the total mixture, wherein: a small weight percentage of an antistatic agent is included, and wherein: a plasticizer is included from about 2% by weight to about 10% by weight of the total mixture.

References Cited UNITED STATES PATENTS 3,382,297 5/1968 Thompson 260-836 3,070,564 12/1962 Roeser 260836 3,222,419 12/1965 Jubilee 260836 3,297,621 1/1967 Taft 260836 3,652,476 3/1972 Fellers 260-830 TW PAUL LIEBERMAN, Primary Examiner US. Cl. X.R.

117124 E, 132 BE, 132 CF; 260--31.8 E, 37 EP, 41 R, 41 B, 41 C, 830 R, 835, 851, 901, DIG. l5 and 16 

